Just tried the 70-200/2.8L IS II on the 1D X with the 600EX-RT. Still locks very quickly, albeit a little more slowly than in a brightly lit room (low-contrast subject, approximately 0.6-0.8 s in good light, 0.8-1.1 s in dim light with the AF assist).

For those having the long lag, what's happening? Repeated AF assist lamp firing, lens hunting back and forth, or just sitting there?

I have yet to test my 7D with my 600. Too busy playing with the 600 and ST-E3-RT. I will and post results. By the way I answered this thread at Canon Forums under the name "digital". I think there was a link in this thread.

Just tried the 70-200/2.8L IS II on the 1D X with the 600EX-RT. Still locks very quickly

I'm obviously talking from the top of my head here (but we're all speculating, and this issue is important to me concerning which ff to get) ... but the 1dx has simply more raw computing power, so maybe it just can calculate the af quicker even though there is less information to work with (weaker af beam)? Or it really is a broken firmware on the 5d3 which will be fixed asap.

I'm obviously talking from the top of my head here (but we're all speculating, and this issue is important to me concerning which ff to get) ... but the 1dx has simply more raw computing power, so maybe it just can calculate the af quicker even though there is less information to work with (weaker af beam)?

Could be. The reason I asked about what is going on during the lag is that very dim light slows metering down (it's why the 7D can only do 4 fps in near-dark, instead of the normal 8 fps). The 5DIII has the same metering sensor as the 7D, but the 1D X is different.

Just tried the 70-200/2.8L IS II on the 1D X with the 600EX-RT. Still locks very quickly, albeit a little more slowly than in a brightly lit room (low-contrast subject, approximately 0.6-0.8 s in good light, 0.8-1.1 s in dim light with the AF assist).

For those having the long lag, what's happening? Repeated AF assist lamp firing, lens hunting back and forth, or just sitting there?

For me the 70-200 f/2.8L IS II without the AF assist will focus in almost an instant even in very low light as long as there is an area of some kind of contrast. For example at wedding receptions when I am photographing the first dances as long as I can focus on where the white shirt meets the grooms neck then I am fine. I also feel really comfortable using AI servo to track the bride and groom entering a very dark reception (so dark I may not be able to see a lot with my own eyes). Again as long as there is some contrast where maybe the white vest meets the black jacket. Now that is great but what if I accidentally slip off an area of contrast and my focus point hits a the dark flat area of the tux? When that happens the lens hunts way out of focus and it takes me a few seconds to recover. In that time I may miss something I really need to get like a smile or a kiss on the cheek. I have tried expanding the point so the surrounding areas are active as well but I found that causes a lot more hunting. One point works the best for me. Now when I used to shoot with the 5D2 I seem to remember being able to focus anywhere because the AF assist would work and it didn't matter if I focused on an area of contrast. That is why I would like the AF assit to work better with the 5D3. When I use the 5D3 the AF assit lamp will flash 3 times usually before the focus will lock and blink red. Now most of the time it focuses much faster than the red confirmation but you really can't trust it all of the time. I would say 90% of the time that area will be in focus before the red confirmation but it may be the time you really need that it will be slightly out of focus. The AF assist flashing 3 full times before focus is way too long in my opinion especially since it was better than that in the past with the 5D2. There has to be a reason and I just want to know why. If there is a trade off because the AF points are smaller I can live with that and like I said before I have learned to work with what I have but part of me feels like I shouldn't have to.

johnnyjohnny

throwing my 2 cents in as i wouldn't even be on this thread if i hadn't noticed a serious intermittent lag, sometimes it just didn't, in red light autofocus confirm...even in decent light. i googled the problem and this was the most impressive documentation and discussion of the issue that i am having.

specifically, there is no real hunting, just a stoppage, or NON focusing...this was happening ever 30 or more shots sometimes for no apparent reason. i noticed mentions of rebooting camera, taking out battery, the latter which i did non my first shoot and it briefly fixed problem.

today was my second use of the 5Diii and i noticed this problem of intermitten non focusing or lag with a tamron 24-70mm 2.8 VC which performed pretty darn good in this dept. on my t2i in very low light. in fact there was NEVER a lag...on the t2i there would be hunting, not much at all...but when there was at least i knew something was going on...the the 5Diii i know nothing (like sgt shultz)...no idea what's going on except that nothing is.

SO, i've tried the fixes suggested, i.e. shutting off af assist beam (tho i was using no flash), and switching af points to include not just the very center, and not even just the extended cross of one box each way, but a full single box ring around the mid af point...if confusing this means all the little boxes in the middle circle.

have it on release priority vs. focus (which seems not to make much diff)...and have noticed i can fully depress shutter without waiting for light confirm of af and the picture will be taken, tho i haven't checked on how in-focus it is.

all this seems to have helped a bit in focusing on low lit spots up to 2 meters around my apt...i've gotten a few complete lags sitting here doing this, but mainly it focuses as quick as with the very good autofocusing t2i...sometimes a less than a sec. lag...but what i hate is that nothing happens...no hunting, just a stall until the af confirm light comes on.

i got the camera for low light street photography of spontaneous journalistic type photography and this problem is a stake in the heart of that work when it happens. it doesn't happen a huge amount of the time but enough that i googled it, and clearly worse than the lowly t2i, which was good in this dept....

i'm very much hoping this is a firmware fixable issue as i've had the camera about 2 months before really using in the field, and have missed any samy's camera return windows...while the camera has full extended coverage, i obviously don't wish to be sending this anywhere...the issue has resolved a bit with the very appreciated info here, but still can be said to exist from some apt shooting tonight...i'd at least like some of you who know canon and problems and issues of this sort, that yes dorothy, there is a santa claus and that he's gonna get canon to fix this through firmware...quick...or at least a lot quicker than my 5Diii autofocuses

I am still following this discussn. I would like to explain how I focus using the the Mark2...which I still have inmy quiver. I do weddings and bar mitzvahs and have to photograph fairly quick action...I always used the oneshot mode and center focus point. In the case of a wedding couple entering the venue...it usually happens prettyquickly...so I would always pre focus on a spot and be ready for the first shot...I would then continually refocuson the couple using the shutter button as they moved toward me while zooming out my 24-105 lens or my17-40 (in a smaller venue). Rarely would any of these shots be out of focus...my main problem was having myflash recycle fast enough to keep up with me. I just did a shot of a young boy running toward me at a golf resortand having him jump in the air several times for an effect. I used the mark2, one shot, center point with my70-200 2.8 is. The shot is so sharp on him that I am making a banner 28" by 72"...his whole body only takesup maybe 12" of space in the shot....every feauture in his face and body are tack sharp....I shot at f4. I would be very hesitant to try this with my mark3...probably would have to use ai focus and make sure I keep that point on the subject.

UPDATE: I've received the replacement 5D3 and will report back after I've used it a bit to compare to the first body I had trouble with.

Curious to hear about your experience with the second body.

OK, I've used the camera a few times now but I didn't do much low light until tonight.

Verdict: This 2nd 5D3 body AF WORKS. Totally different experience. It works as I think it should. If the last camera worked like this camera, I likely never would have visited this thread for more than casual curiosity.

I've done nothing scientific or really anything different than the last camera. I just set the menu settings the same as my other cameras and used it like I use any camera. I used a 24-70 f/2.8L lens tonight. I also tried a 24-105 f/4L. Both worked virtually the same with regard to AF Lock in low light.

Didn't matter...- ... what setting the AF Assist light was set to (either OFF or ON)- ... whether a flash was attached or not- ... whether the flash was turned on or not- ... if it was a Canon flash or a Sunpak RD2000- ... if I hold a beer in one hand, hold the camera steady with both hands, or balance the beer on top.

The camera focused as I would expect in all cases. Nothing took longer than 2/3 sec except the almost dark rolling cart, it took about 1 sec with the AF Assist lamp on a 580EX-II flash. No ridiculous and maddening focus hunting.

If I try to get AF Lock in a semi-dark environment with AF Assist = OFF, the camera will either refuse to try (Focus Hunt = Off) or never AF Lock (Focus Hunt = On) which I consider normal. If I then turn on the AF Assist, it focuses in 1/2 - 1sec. I've also noticed that the AF Lock/Hunt/Red AF point red blink doesn't even happen if the focus hasn't changed. I wish it would still blink anyway.

So far this is only a few hundred shots in to this body. Some have complained that their camera started off fine and then suddenly got worse. All I know is it works better and gives a much better result than the 1st body and I am glad I exchanged it!

Thanks to this forum for helping me conclude that there are some folks that have had no problems and others that have exp. similar problems. I was pretty doubtful I would get a better replacement body but so far, I think I did!

Here are some small JPGs straight out of the camera SD slot, no changes whatsoever. Candlelight, 40W lamp in background and then very dark foyer using AF Assist lamp and then flash fired.

hammy

1Dx / 85 1.2L 2 + 600ex rt - i had a difficulty getting focus in low light at a park. My images turned out to be blurry zoomed in . I thought to myself this will be horrible for low light wedding dances , etc . Trying to take pictures with kids running around in low light is extremely difficult. Wished it has IS

But I understand it's your 1st replacement, but 2nd 5d3 body :-> ? ... anyway, things tend to get more confusing with more data w/o a scientific approach, and the latter is hard to achieve in these cases.

To sum it up: If what you're writing is correct, that means your 600rt is working fine but for the 5d3 this means the possibility of broken hardware: either randomly, semi-randomly by timebomb (deterioration of some part) or systematically (that's what you get as an early adopter :-p ... but maybe people should post their rough serial# and purchase date).

I fear to work this out we need someone with a broken and a working 5d3 camera body at the same time or at least shooting the exact same situations and memorizing/noting what the exact difference is with what lenses, lighting conditions and focal distances

OK, I've used the camera a few times now but I didn't do much low light until tonight.

Verdict: This 2nd 5D3 replacement body AF WORKS. Totally different experience. It works as I think it should. If the last camera worked like this camera, I likely never would have visited this thread for more than casual curiosity.

I've done nothing scientific or really anything different than the last camera. I just set the menu settings the same as my other cameras and used it like I use any camera. I used a 24-70 f/2.8L lens tonight. I also tried a 24-105 f/4L. Both worked virtually the same with regard to AF Lock in low light.

Didn't matter...- ... what setting the AF Assist light was set to (either OFF or ON)- ... whether a flash was attached or not- ... whether the flash was turned on or not- ... if it was a Canon flash or a Sunpak RD2000- ... if I hold a beer in one hand, hold the camera steady with both hands, or balance the beer on top.

The camera focused as I would expect in all cases. Nothing took longer than 2/3 sec except the almost dark rolling cart, it took about 1 sec with the AF Assist lamp on a 580EX-II flash. No ridiculous and maddening focus hunting.

If I try to get AF Lock in a semi-dark environment with AF Assist = OFF, the camera will either refuse to try (Focus Hunt = Off) or never AF Lock (Focus Hunt = On) which I consider normal. If I then turn on the AF Assist, it focuses in 1/2 - 1sec. I've also noticed that the AF Lock/Hunt/Red AF point red blink doesn't even happen if the focus hasn't changed. I wish it would still blink anyway.

So far this is only a few hundred shots in to this body. Some have complained that their camera started off fine and then suddenly got worse. All I know is it works better and gives a much better result than the 1st body and I am glad I exchanged it!

Thanks to this forum for helping me conclude that there are some folks that have had no problems and others that have exp. similar problems. I was pretty doubtful I would get a better replacement body but so far, I think I did!

Here are some small JPGs straight out of the camera SD slot, no changes whatsoever. Candlelight, 40W lamp in background and then very dark foyer using AF Assist lamp and then flash fired.

[/quote]

Rusty...that's good to hear! Your experience is precisely why I never buy refurbished items. ( your original camera will eventually be sold as refurbished and someone else will inherit the problem)

I'm curious, do you have image stabilization turned on or off when you shoot with beer in hand?

Enjoy your new camera!

PS...the shot of the roller cart is truly a work of art and a masterpiece

I remember reading in this post from a couple people that their AF would hunt and then just "give up" and never acquire focus in poor available light. For those of you that posted this, try checking your AF setting "lens drive when AF is impossible" and make sure it is set to "ON"

I mention this because when I first bought my 5d3 I had inadvertently turned this setting to OFF (or it came that way as a default, I'm not sure) and I paid the price later when I was in a low light situation and my 5d3 would just give up and quit focusing....took me a while to go through the settings and figure out that this setting was the issue. The key here is that it only became an issue when I was in poor light.

But I understand it's your 1st replacement, but 2nd 5d3 body :-> ? ... anyway, things tend to get more confusing with more data w/o a scientific approach, and the latter is hard to achieve in these cases.

To sum it up: If what you're writing is correct, that means your 600rt is working fine but for the 5d3 this means the possibility of broken hardware: either randomly, semi-randomly by timebomb (deterioration of some part) or systematically (that's what you get as an early adopter :-p ... but maybe people should post their rough serial# and purchase date).

I fear to work this out we need someone with a broken and a working 5d3 camera body at the same time or at least shooting the exact same situations and memorizing/noting what the exact difference is with what lenses, lighting conditions and focal distances

Thanks Marsu42, I removed the 'replacement' term, it was late and that was confusing. I only have a 580EX-II, not a 600rt. I agree, my experience seems to indicate poor QA, bad parts or a combination of the two. I held out hope because some have reported no problems. I'll definitely keep watching and report my continued use experience. And yes, I've been too busy to do anything extremely precise or methodical but this body definitely works like one would expect. I'm still not totally blown away by the low light focus w/o AF Assist but at least it now works better than my other (older) cameras which wasn't the case before.